Avian eggshells exhibit some of the most diverse and fascinating arrays of complex biological variability within the animal kingdom. The variation seen in eggshell colour and maculation (pigment spots), for example, can be found between species, within species, and even between eggs in a clutch from the same female. Eggshell maculation has fascinated scientists for decades, and many functional explanations for this maculation have been posited including crypsis, thermoregulation, microbial defence and sexual-signalling. While the variation and function of eggshell maculation has received much attention, the actual structure of the eggshell itself has received comparatively little focus. The relatively few studies that have investigated eggshell structure, particularly that of the egg surface, have found large variation in surface-structures and shell thickness. However, little is known about how these structures function, or rather, what their true function is. This project aims to characterise eggshell surface structure along the avian phylogenetic tree, and determine – through novel mechanical and structural engineering approaches – how different eggshell surface structures function. Bird eggs offer a fascinating model system, as birds breed on all seven continents on Earth; at altitudes greater than 4000 m above sea level, in temperatures ranges between -40°C and 50°C, and in environments varying from water-saturated to extremely xeric. Egg size can range from 1.4 kg to 0.4 g (for Common Ostriches Struthio camelus and Vervain Hummingbirds Mellisuga minima, respectively), while clutch size can vary from a single egg to broods of over fourteen.